1. Technical Field
The invention relates to the field of purification of natural and waste waters, in particular, to electrochemical devices of a diaphragm type with integral or loose electrodes, and more particularly, to an electrolyzer for removing fluorine-containing impurities from water.
The electrolyzer makes it possible to obtain easily removable products of electrochemical reactions with adsorbed fluorides, ions of heavy, alkali and ferrous metals, petroleum products and other readily dispersed agents.
2. Description of the Related Art
Known in the art is an electrolyzer for purifying liquid media from impurities, which comprises a casing divided by a semi-permeable dielectric diaphragm into two chambers, namely, an anode chamber furnished with an electrochemically insoluble electrode and a cathode chamber with an electrode from metal or an alloy capable of chemically dissolving in alkali to form a coagulant, e.g., from aluminium or duralumin. The given electrolyzer can be used for removing fluorine-containing impurities from water. However, this electrolyzer is characterized by a low efficiency of using the products of electrode reactions occurring on the anode or cathode. Since the anode is made from an electrochemically insoluble material, the products of electrochemical dissolution of the anode actively sorbing fluorides or other impurities will not be generated (introduced) into the water being treated. In the prior art electrolyzer the cathode is made from an aluminium-containing metal (alloy) chemically soluble in alkali, therefore, the products of electrode reactions occurring at the cathode, particularly, hydroxyl groups OH.sup.- cannot be used effectively enough in the electrolyzer to purify fluorine-containing waters. These hydroxyl groups of of the known concentration create conditions of the hydrate-formation of magnesium ions (Ma(OH).sub.2) whose flakes actively absorb fluorides. Besides, upon dissolving the surface of an aluminium-containing integrated electrode (cathode) in an alkali solution, a layer of gel-like coagulant is formed on this surface which results in screening the surface of the electrode (cathode) by the products of its chemical dissolution which, in turn, decreases the rate of electrochemical generation of OH.sup.- ions, concentration of magnesium hydroxide and the dissolution of the cathode to form a coagulant, as a result of all this the voltage in the electrolyzer is increased and the degree of purification is decreased.
Also known in the art is an electrolyzer for removing fluorine-containing impurities from water, comprising a casing divided by a semi-permeable dielectric diaphragm into two chambers, namely, an anode chamber accommodating an integrated electrode from an electrochemically insoluble material and a loose charge from particles of electrochemically soluble material, both connected with the positive terminal of a current source, and a cathode chamber accommodating an integrated electrode from an electrochemically insoluble material which is connected to the negative terminal of a current source, branch pipes for feeding and removing the water being purified which communicate with the cathode chamber. In so doing, the integrated electrode may be made either from a material chemically insoluble in an alkaline solution, e.g., a steel sheet, or a material chemically soluble in an alkaline solution, e.g., an aluminium (duralumin) sheet or rods.
However, when using an electrode from a material chemically insoluble in an alkaline solution, fluorides, or fluorides and ions of heavy metals and/or easily-dispersed suspended organic and/or mineral substances simultaneously present in the solution (Water) are removed only due to the products of electrode reactions taking place in the anode chamber (products of electrochemical dissolution of a loose charge). The products of electrochemical processes occurring on the electrode connected with the negative terminal of a current source - at the cathode are not used in purifying water from fluorides. This entails a higher electric power consumption and a greater size of apparatus employed for purification of fluorine-containing waters.
When using an integrated electrode from a material chemically soluble in an alkaline solution in the cathode chamber, the surface of this material is coated with the products of its dissolution. This increases the voltage in the electrolyzer and brings about passivation of the electrode connected with the negative terminal of the current source. As this electrode is passivated, the supply of OH.sup.- ions to the solution (water being treated) is cut off, i.e., the formation of alkali according to the reaction of electrochemical decomposition of water is terminated and this, in turn, results in the termination of electrochemical dissolution of loose charge arranged in the anode chamber (alkali and the products of dissolution of the charge arranged in the anode chamber are formed in equivalent quantities) and the process of water purification is discontinued.